1. The isolated strips of guinea-pig, fowl and reptiles (snake and tortoise) showed consistenly excitatory responses to PGE₁ and E₂, which were dose-dependent. 2. Frog intestine revealed inhibitory responses to both PGE₁ and PGE₂ except a small of PGE₂ (1-10 ng/ml) caused slight contraction. 3. The intestines of pieces showed inconsistent responses to PGE₁ and E₂. In fresh-water fish(carp), PGE₁ produced relaxation under the dose of 50 ng/ml, and contraction by the large doses, but PGE₂ consistently caused contraction in dose-dependent manner. However, the strips of sea-water fish revealed the different responses to PGE compound: PGE₁ caused relaxation and PGE₂ conversly contraction even though in small degree. 4. These results that there are genera differences in the responses of the longitudinal strips of intestine to PGE₁ and PGE₂ was assumed to be possibly correlated with evolutionally primitive function of gut.